Second Generation Raytheon Stirling/Pulse Tube Hybrid Cold Head Design and Performance

Abstract

Raytheon is in initial test of a second generation two-stage Stirling/pulse tube hybrid cold head for use in long life space cryocoolers. The Stirling/pulse tube configuration provides excellent thermodynamic performance by optimally combining the strengths of both technologies. The cold head is designed for optimal performance at a second stage temperature of 40 K and a first stage temperature of 110 K with nominal capacity of 1 W at the lower stage and simultaneous 7 W at the upper stage. The inherent load shifting capability of this configuration permits efficient operation of the cooler over a wide range of temperatures and heat loads. Load shifting is accomplished through varying the phase angle of the Stirling displacer piston relative to the pressure wave. Load shift data on the new cold head is provided. Lessons learned from the testing of the initial brass-board regarding component sizing have been incorporated into this second generation design. The quantitative improvement provided by those design changes is presented. The second generation cold head design is currently being incorporated into a flight design warm-end expander motor assembly with Oxford-class flexure and clearance technology typical of Raytheon flight-qualified production cryocoolers for space. The expander is driven by an Oxford-class compressor of similar design legacy to other Raytheon designs.